Arch has been working with Valve on various build system improvements for some time [0], which as I understand it are targeted at making it more feasible for them to eventually support more architectures [1]. This doesn't release for several months; I wonder if there'll be an official Arch Linux ARM by then?
[0]: https://lists.archlinux.org/archives/list/arch-dev-public@li...
[1]: https://news.ycombinator.com/item?id=41696041